The proposed research involves two goals: identification and verification of non-invasive outcome measures that reflect autonomic nervous system activity and verification of the role of the sympathetic nervous system (SNS) in the maintenance of primary hypertension. The design is a form of the time series experiment with the introduction of three experimental variables sequentially that are expected to increase or decrease sympathetic activity. Sympathetic nerve discharge will be measured directly and will serve as the "gold standard" for non-invasive measures of SNS activity (i.e., blood pressure, heart rate, galvanic skin resistance, peripheral skin temperature, pupil size, frontalis muscle activity, and catecholamine levels). Two groups of female subjects will be studied: healthy normotensives and those with primary (essential) hypertension. Receiver Operating Characteristic (R0C) Curves will be generated to display the sensitivity and specificity of each of the indirect measures of SNS activity. Based on the relationship between SNS activity and blood pressure, it will be possible to identify a group of hypertensive subjects in which the SNS is involved in the maintenance of hypertension. Such patients are much more likely to respond to pharmacologic and non-pharmacologic therapy which addresses the overactivity of the SNS than are other hypertensive patients.